From 9f8381ff71253fdba018e0bc2e88555fdfefe35c Mon Sep 17 00:00:00 2001
From: German Khokhlov <ouchlock@gmail.com>
Date: Tue, 3 Nov 2026 22:56:24 +0400
Subject: [PATCH] Check a parked renderer's real WebGL context before reuse and
 rebuild it when the context is lost

---
 src/standalone/rendererCache.js       |  7 ++++++-
 src/standalone/rendererCache.test.mjs | 11 +++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/src/standalone/rendererCache.js b/src/standalone/rendererCache.js
index 49db694df..9347ab7a3 100644
--- a/src/standalone/rendererCache.js
+++ b/src/standalone/rendererCache.js
@@ -8,7 +8,12 @@ export function createRendererCache() {
     const host = document.getElementById('cesiumContainer');
     let entry = idle.get(kind);
     idle.delete(kind);
-    if (entry?.lost) {
+    // loseContext() takes effect before its queued DOM event is delivered.
+    // Check the existing context too, before resuming a parked render loop.
+    const canvas = entry?.scene.engine.host.canvas;
+    const context =
+      canvas?.getContext?.('webgl2') ?? canvas?.getContext?.('webgl');
+    if (entry && (entry.lost || context?.isContextLost())) {
       entry.dispose();
       entry = null;
     }
diff --git a/src/standalone/rendererCache.test.mjs b/src/standalone/rendererCache.test.mjs
index aca7cc207..4b4b2cddc 100644
--- a/src/standalone/rendererCache.test.mjs
+++ b/src/standalone/rendererCache.test.mjs
@@ -54,7 +54,8 @@ test('a parked renderer is reused, but a lost context is disposed before rebuild
   assert.equal(first.engine.host.container.isConnected, true);
   cache.retain('navara');
   release();
-  first.engine.host.canvas.dispatchEvent(new Event('webglcontextlost'));
+  // The WebGL context is already lost, but its DOM event has not fired.
+  first.engine.host.canvas.getContext = () => ({ isContextLost: () => true });
   const second = await open();
   assert.notEqual(second, first);
   assert.equal(released, 1);
@@ -66,7 +67,13 @@ test('a parked renderer is reused, but a lost context is disposed before rebuild
   await assert.rejects(open(), /resume failed/);
   assert.equal(second.engine.host.container.isConnected, false);
   assert.equal(released, 2);
+  const eventLost = await open();
+  cache.retain('navara');
+  release();
+  eventLost.engine.host.canvas.dispatchEvent(new Event('webglcontextlost'));
   const third = await open();
+  assert.notEqual(third, eventLost);
+  assert.equal(released, 3);
   third.suspend = () => {
     throw new Error('suspend failed');
   };
@@ -74,5 +81,5 @@ test('a parked renderer is reused, but a lost context is disposed before rebuild
   assert.throws(release, /suspend failed/);
   assert.equal(third.engine.host.container.isConnected, false);
   cache.clear();
-  assert.equal(released, 3);
+  assert.equal(released, 4);
 });